Developers availability: The architecture must have a developer-available (i.e. debian.org) machine that contains the usual development chroots (at least stable, testing, unstable).

There is escher.debian.org, but this host is not accessible to developers for 5 months.

Users: The architecture needs to prove that developers and users are actually using it. Five Developers need to certify in that they're activly developing on this architecture, and it needs to be demonstrated that at least 50 users are using the platform.
We are counting users for the second criteria, not machines; e.g., one s390-installation with 50,000 users fullfils the user criterion just fine.

The University Computer Club at UWA has some Alphas running Debian. "We have one Alpha running Debian with a GNOME desktop for use by club members, and at least one other running Debian Sarge in the machine room. I'm not sure how many members the club currently has but there would be at least 5--10 who regularly use the Alphas." (?CameronPatrick)

The mailserver of the Institute for Theoretical Physics at the University of Hanover is running Debian GNU/Linux, currently serving 38 permanent users plus several short term users. In addition, we have got six Alpha (EV67) which are still used for numerical computations. I cannot tell the exact number of users for them, but it's between two and five. (?CarstenLuckmann)

Porters and Upstream support: There is support by the porters and upstream. This is especially true for the toolchain and the kernel.
This criterion doesn't forbid that Debian's and upstream's support is handled by the same persons.

Linux, gcc, binutils, and glibc are all maintained upstream by Richard Henderson, who has write access to all four repositories, so they usually work with unmodified upstream sources. Gdb does not have a designated Alpha maintainer, but works OK at the moment.

Archive coverage: The architecture needs to have successfully compiled the current version of the overwhelming part of the archive, excluding architecture-specific packages.
Our back-of-the-envelope number is 98% of the archive. We don't have a good way to measure an architecture's compliance with this yet, but we'll work on figuring that out; of course we will exclude hardware-specific packages and buggy packages with severe portability issues in optional/extra packages, but porters must take responsibility for working with maintainers to fix portability issues.

the graphs on http://buildd.debian.org/stats/ show that Alpha is pretty stable shortly above 98%. The typical Alpha build failures are 64-bit issues which other architectures (ia64, amd64) have as well

Archive cleanliness: All binary packages need to be built from unmodified sources (i.e. from the source found in the ftp archive), and all binary packages need to be built by debian developers.
That's just what's always true. Here only for completness.

This is true.

Autobuilder support: The architecture is able to keep up with unstable with not more than two buildds, has redundancy in the autobuilder network, keeps their autobuilders running for 24x7, has autobuilders acceptable for security support.
We need of course autobuilders, and they need to be able to keep up.
As mentioned multiple times, there is a nontrivial cost to each buildd, which increases super-linearly; there have been cases in the past where this resulted in ports with many autobuilders slacking when updates were necessary.
Redundancy is necessary just in case some buildd has hardware failures or whatever else. History told the release team that redundancy is really necessary. Noone in the release team wants again to track where a box in europe is just located, and prod some developer in that country to pick the box up, because that's largest blocker of the next stable release.
Of course, autobuilders can have hardware maintainence. But the autobuilers need to be able to run 24x7, and the need to be generally up all the time (and thanks to the redundancy above, there should always be an autobuilder currently running).